A block is a sequence of bytes (for example, a 512-byte block of data).
Block-based storage interfaces are the most common way to store data with
rotating media such as hard disks, CDs, floppy disks, and even traditional
9-track tape. The ubiquity of block device interfaces makes a virtual block
device an ideal candidate to interact with a mass data storage system like Ceph.

Ceph’s block devices deliver high performance with infinite scalability to
kernel modules, or to KVMs such as QEMU, and
cloud-based computing systems like OpenStack and CloudStack that rely on
libvirt and QEMU to integrate with Ceph block devices. You can use the same cluster
to operate the Ceph RADOS Gateway, the
CephFS filesystem, and Ceph block devices simultaneously.

Important

To use Ceph Block Devices, you must have access to a running
Ceph cluster.